Great question and here's the best deal i've found after reading and reading and scouring the net.
www.b-p-p.com
They'll sell you a Mega 16/15/X with a Castle Creations Phoenix 25 for $135. Talk to troy. He'll take 10% off if he doesn't have it in stock. the three turn is there now... the 4 turn is due in 2 weeks. Difference is 3 turn = more speed 4 turn = more thrust... flip a quarter
Good luck